The present invention relates to a method and apparatus of forming moldable integrated truss structures and to composite structures resulting from incorporating such truss structures between outer framing elements, sheets, skins or by incorporating strengthing structures within the truss structures.
Numerous efforts have been made in the past for providing improved truss structures and for reducing the time and expense involved in manufacturing such truss structures. As is known in the art, truss structures typically are utilized to provide support for a thin material such as a metallic skin, a floor, roof or wall or other such surface which is not capable by itself of supporting shear, bending and axial loads in various directions. Most truss structures, are formed of a plurality of diagonal strut members which are joined together by means of rivets, welds, or a nut and bolt arrangement. Examples of such prior art truss structures may be found in Bunker, U.S. Pat. No. 2,123,931 and Troutner, U.S. Pat. No. 3,541,749. In each of these patents, a truss structure is disclosed which requires a substantial amount of labor to join the strut beams to one another to provide a truss which is capable of supporting forces acting thereagainst. Another example of such a truss structure is disclosed in Snyder et al, U.S. Pat. No. 3,415,027 wherein an unsymmetrical truss structure is formed of a plurality of steel beams which must be joined to one another by means of a riveting process which requires a substantial amount of labor.
Kastan disclosed in U.S. Pat. No. 2,791,386 a symmetrical truss structure having a plurality of strut elements joined at bosses at the top and bottom of the truss. The truss structure is capable of transmitting shear, bending and axial loads in any direction and is used for the cores of aircraft wings, structural panels and box type structural beams. There is no disclosure of a method of forming this truss structure as an integral unit, such as, by means of an injection molding process.
Other forms of reinforcing structures are illustrated in Pajak, U.S. Pat. No. 2,609,068 and Plumley et al, U.S. Pat. No. 2,849,758 wherein a honeycomb structure is disclosed. The drawbacks to a honeycomb structure are that substantial manual labor is required to join the honeycomb elements together and once formed it is difficult to provide an insulating means for the structure if such is desired, i.e. insulation or foam cannot be injected through the honeycomb structure to provide an insulation medium.
Each of the aforementioned types of truss structures have the drawback that each require a relatively large amount of manual labor for forming the truss structure which inherently drives up the cost of such structures. Therefore, there is a need in the art for a simplified truss structure which can be formed with a minimum of labor to thereby reduce the cost of such structures. Patents which show types of mold structures include Schavoir, U.S. Pat. No. 1,409,591, Yellin, U.S. Pat. No. 2,566,817, Cohan, U.S. Pat. No. 3,333,300, Karlyn, U.S. Pat. No. 3,790,371, Taketa, U.S. Pat. No. 3,871,611 and Lipscomb, Canadian Patent No. 883,932.
It is another object of this invention to provide an apparatus for forming an integrated truss structure.